You can use a 3rd party service called MigrationWiz.com, it's used by F100s to migrate their corporate email, but also works for consumer migrations. I believe

You can use a 3rd party service called MigrationWiz.com, it's used by F100s to migrate their corporate email, but also works for consumer migrations. I believe at one point it was done via IMAP, but Google changed their APIs and you may have to grant greater access. I could be wrong here, it's been a few years since I last worked there. Hope this is helpful.